HAMMER2_XOPFIFO_MASK
chain = fifo->array[fifo->ri & HAMMER2_XOPFIFO_MASK];
fifo->errors[fifo->wi & HAMMER2_XOPFIFO_MASK] = error;
fifo->array[fifo->wi & HAMMER2_XOPFIFO_MASK] = chain;
chain = fifo->array[fifo->ri & HAMMER2_XOPFIFO_MASK];
error = fifo->errors[fifo->ri & HAMMER2_XOPFIFO_MASK];